Cell protein production Biology ATAR & General Human Biology ATAR & General

Keywords DNA Ribosomes Protein synthesis tRNA mRNA Transcription RNA polymerase Template strand Coding strand Codon Intron Exon Ribosomes tRNA Anticodon Translation Start codon methionine Protein structure Endoplasmic reticulum (ER) Golgi bodies

What does DNA code for? DNA carries the instructions for making proteins These instructions are organised into segments called genes. Genes are divided into 2 categories: Coding genes (exons) Non-coding or regulating genes (introns)

Introns & exons Introns Introns can be thought of as the chef in the kitchen. The chef decides when the cake should be made (eg. for a birthday), what kitchen appliances are to be used, how the ingredients are to mixed, what temperature the oven needs to be and how long the cake should be baked for. Exons Exons can be thought of as a recipe, with a list of ingredients and instructions. The ingredients being the amino acid codons, and the instructions being the sequence of assembly.

Review: functions of proteins Proteins have many different functions: Structure: the protein keratin gives strength to hair, nails etc. Transport across membranes: some proteins form channels in cell membranes to aid the transport of molecules Communication: many hormones are proteins. Cell metabolism: enzymes are proteins . Enzymes help speed up the chemical reactions in a cell. Recognition: proteins in the cell membrane are unique to a particular person Movement: protein molecules are able to change shape and this is the basis for the movement of structures within the cell.

Proteins Proteins are made up of amino acids. There are 20 different types of amino acids in the body Most proteins are very large molecules consisting of hundreds to thousands of amino acid chains. Coding genes (exons) specify the number and type of amino acids and the order in which they are to be assembled.

Protein synthesis Transcription Occurs in the nucleus Enzyme involved: RNA polymerase Product: mRNA Protein synthesis occurs in 2 parts Transcription Translation Translation Occurs at the ribosome Molecules involved: mRNA & tRNA Product: protein

Transcription, translation & RNA The DNA molecule is too large to leave the nucleus Another molecule called ribonucleic acid or RNA is made RNA carries the information for only one gene at a time RNA transcribes and translates this information to make one protein This happens at the ribosome in the cytoplasm RNA consists of a Ribose (a sugar) Phosphate Nucleotide base RNA is slightly different to DNA. Instead of thymine it has uracil

DNA vs. RNA Thymine (+C) Uracil (-C) deoxyribose ribose

Double strand Single strand

Transcription, translation & RNA There are 2 types of RNA Messenger RNA (mRNA) Transport RNA (tRNA) mRNA takes the code from the DNA, across the nuclear membrane, to the ribosome in the cytoplasm tRNA helps to build the protein by bringing the amino acids to the mRNA at the ribosome

Transcription Transcription is the formation of the mRNA strand It occurs in the nucleus The genetic instructions are copied from the DNA to the mRNA molecule The process is very similar to DNA replication

Transcription RNA polymerase is the enzyme that ‘unzips’ the double stranded DNA It then transcribes (copies) the bases from one strand of DNA to make a complementary strand of mRNA At the end of the gene there is a sequence of bases that tells the RNA polymerase to stop copying and the mRNA molecule is released

Transcription

Transcription Only one of the strands of DNA is copied during transcription This strand is called the template strand The other strand is called the coding strand Because the bases always form complementary pairs, the order of bases in the mRNA molecule will be the same as in the coding strand, but opposite to the template strand

Transcription Remember, DNA contains introns and exons The mRNA that has been copied contains both introns and exons Introns must be removed before the mRNA can be used to assemble amino acids into a protein

Introns and exons Exons DNA mRNA Intron Intron NIH - National Human Genome Research Institute

Translation Every mRNA molecule has a starting codon and a stopping codon This ensures that protein synthesis starts at the correct end of the mRNA molecule Translation is the process of synthesising a protein from the information contained within the mRNA It occurs at the ribosome It involves both mRNA and tRNA

Translation The ribosome then moves along the mRNA and pulls it through like a ribbon, reading the bases as it goes

Translation, codons & anticodons Every 3 base pairs form a codon Each unique codon is associated with one type of amino acid There are 20 types of amino acids in the body tRNA molecules carry the complementary codon These are called anti-codons There are 20 types of tRNA molecules, each with its unique anti-codon on one end and carrying the corresponding amino acid on the other end

Translation The tRNA molecules bring the individual amino acids to the mRNA/ribosome complex to be joined together to form the protein The anti-codon on a tRNA molecule binds to the complementary codon on the mRNA molecule

Translation The amino acids carried by the tRNA are joined together so the protein is assembled in the right order Each bond formed between the amino acid requires 1 ATP Once the tRNA has delivered its amino acid it detaches from the ribosome

Translation NIH - National Human Genome Research Institute

Protein structure After a protein has been synthesized, it must then be organised into a particular shape Protein shape is very important for the correct functioning of the protein Proteins have 3 or 4 levels of complexity in their structure

Protein structure Primary structure: is the sequence of amino acids in the chain that makes up the protein Secondary structure: this is either a coiled or folded shape that is brought by bonds between different parts of the amino acid chain Tertiary structure: this is formed by further bending and folding of the protein into globular or fibrous shapes Quaternary structure: when 2 or more chains of amino acids interact

Packaging of proteins If proteins are to be used outside the cell, they must be packaged for secretion After proteins are made at the ribosome, they travel through the ER into the golgi bodies where they are modified and packaged via exocytosis

Lipid and carbohydrate synthesis DNA only contains code for the manufacture of proteins However, it contains code for the production of enzymes (which are proteins) and therefore DNA indirectly controls the synthesis of lipids and carbohydrates

PROTEIN SYNTHESIS – TRANSLATION & TRANSCRIPTION Class resources https://www.youtube.com/watch?v=h3b9ArupXZg&index=46&list=PL7A750281106CD067   Bozeman Science Transcription and Translation: 12 mins Student resources http://www.egs.ie/files/translation.swf http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein+Synthesis http://www.wiley.com/college/test/0471787159/biology_basics/animations/fromGeneToProtein.swf http://highered.mheducation.com/sites/dl/free/0073525634/291136/mRNA_synthesis.swf http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf